Fibrous glass products have been manufactured for many years using precious metal bushings, or glass feeders. Such glass feeders include a foraminous bottom plate or wall, commonly referred to in the art as a tip plate, which retains a molten pool of glass and which issues a stream of molten glass through the openings thereof. By suitable means the streams of glass are then attenuated and collected in the form of fibers. Such glass feeders, or bushings, must be chemically resistant to the action of molten glass and must be dimensionally stable at high operating temperatures, for example, temperatures in the range of about 1000.degree. C. to 1600.degree. C. Dimensional stability of the foraminous bottom plate or tip plate, particularly in respect to its sag or creep rate, is of particular significance as deformation of the bushing will result in an improper heat distribution across the top plate and can also result in misalignment of the openings of the foraminous bottom wall and enlargement thereof. Obviously, this has a detrimental impact on the quality and cost of glass being manufactured and requires the replacement of the glass feeder. Because precious metals are involved, frequent replacement of the bushing is unsatisfactory because of cost including fabrication and lost production. Consequently, there is a need in the art to provide for a bushing which will have greater dimensional stability and greater resistance to creep at elevated temperatures.
In accordance with the present invention, applicant provides for a glass feeder which has superior high temperatures stress-rupture and creep properties and which is resistant to glass corrosion and oxidation.
Thus, in accordance with one feature of this invention an improvement is provided in methods and apparatus for manufacturing fibrous glass products which methods comprise maintaining a pool of molten glass in a glass feeder having a foraminous bottom plate with a transverse axis shorter than the longitudinal axis thereof, and attenuating a glass stream issuing from said foraminous bottom plate into a glass fiber. The improvement resides in employing a bottom plate which is formed of a dispersion strengthened precious metal, or alloy, with the plate having a lower creep rate along its transverse axis than its longitudinal axis. That is, the bottom plate or tip plate is formed of a creep resistant dispersion strengthened precious metal sheet which is anisotropic with respect to its creep rate and the feeder is so formed that the axis of the tip plate with the minimum creep rate corresponds to the transverse, or width, dimension whereas the axis with the higher creep rate corresponds to the length, or longitudinal axis of the bottom plate.